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Terminology

The term moyamoya disease should be reserved for an idiopathic, sometimes familial, condition, which leads to characteristic intracranial vascular changes. Numerous entities have been described which mimic the appearance, in which case the term moyamoya phenomenon, syndrome or pattern is used.

This article concerns itself with moyamoya disease. For a list of conditions that can mimic moyamoya please refer to the article on moyamoya syndrome, or the differential diagnosis list at the end of the article.

Epidemiology

Moyamoya is a disease of children and young people, with a bi-modal age distribution 6:

early childhood: peak ~4 years of age (two-thirds)

middle age: 30-40 years of age (one-third)

The condition was initially described in Japanese patients, where it is still most common, in which 7-10% of cases are familial.

Clinical presentation

Presentation is to some degree age dependent. In children hemispheric ischaemic strokes are most pronounced, whereas in adults haemorrhage from the abnormal vessels is more common 6. Watershed infarcts are also very commonly identified.

Radiographic features

Moyamoya disease affects the bilateral distal ICAs and circle of Willis. Up to 18% of patients with moyamoya may present with unilateral angiography-documented disease 8.

Small abnormal net-like vessels proliferate giving the characteristic "puff of smoke" appearance on direct angiography. CTA and MRA is not always able to demonstrate this appearance on account of lower flow and spatial resolution.